1. Field of the Invention
The invention relates generally to the field of seismic surveying. More specifically, the invention relates to devices for navigating a marine seismic source array suspended in water from a floatation device to avoid navigation hazards.
2. Background Art
In marine seismic surveying, a seismic energy source is used to generate seismic energy in the form of acoustic pulses or waves in a body of water such a lake or the ocean. The seismic energy travels downwardly in the water, through the water bottom, and through the Earth formations underlying the water bottom. Part of the energy passing through the Earth formations underlying the water bottom is reflected upward from acoustic impedance boundaries in the Earth formations. The upwardly traveling seismic energy is detected by sensors such as hydrophones towed in one or more streamer cables disposed near the water surface, or by sensors disposed in cables along the water bottom. The sensors convert the detected energy to electrical or optical signals. The electrical or optical signals are then conditioned and interpreted to provide information both as to the composition and the structure of the various subsurface Earth formations. Such information is used particularly to determine the possibility that such Earth formations may contain mineral deposits such as hydrocarbons.
The most frequently used marine seismic energy source known in the art is an “air gun array.” A typical air gun array is a plurality of individual air guns of different sizes towed behind a seismic survey vessel or a source vessel. The air guns are ultimately suspended from a buoy, float or similar flotation device. The flotation device is typically coupled to a frame or similar substantially rigid structure so as to suspend the frame in the water. Individual air guns forming the array may be suspended from the frame by cables or chains of selected length so that the individual air guns are operated at a selected depth in the water. In air gun arrays known in the art, the floatation device may be steerable in the plane of the surface of the water, but remains proximate the surface of the water by reason of the buoyancy of the flotation device.